The Irradiation Facility at Fox Chase Cancer Center (FCCC) manages the shared use of ionizing radiation sources according to procedures mandated in our license from the Nuclear Regulatory Commission (NRC). Management and maintenance of these potentially dangerous, costly devices ($100,000-$200,000 each) as a shared resource for multiple users facilitates administration, quality assurance, safety and regulatory compliance. The Facility consists of two different irradiators, each sited optimally for its specific use. They produce fields of Cesium-137 gamma-rays to irradiate molecules in solution, cell cultures, rodent tumors or normal tissues for studies of radiobiologic mechanisms, to suppress immune response, to induce DMA damage and/or mitotic arrest, and to sterilize cell and drug preparations. The Shepherd Model 280 irradiator is situated in the Laboratory Animal Facility and used mainly for whole body irradiation of animals used in immunobiology research (see Hayakawa et al., J. Exp. Med. 197:87-99, 2003; Allman et al., J. Immunol. 167:6834-6840, 2001). The panoramic Shepherd Model 81-14R irradiator is situated in the basement of the Reimann Building. It was used 223 times in 2003 primarily for the irradiation of cells (see, for example, Katz et al., J. Virol. 76:5422-5434, 2002; Mu et al., Int. J. Radiat. Oncol. Biol. Phys. 58:336-343, 2004). Oversight of Facility operation is provided by the Facility Manager, Facility Director, Radiation Safety Officer, Radiation Safety Committee, FCCC Administration and the NRC. Facility staff operate various radiation dosimeters to accurately determine the dose to experimental set-ups and is available to FCCC investigators for planning radiation experiments, to assist infrequent users, for training individuals to become qualified irradiator users in accord with NRC and other safety regulations and for overseeing the annual maintenance and quality assurance of equipment. Inventories of the radioactive sources are made at intervals determined by the Homeland Security threat level. Over the last Core grant cycle, the Facility was used by 24 peer-reviewed funded investigators from ten FCCC research Programs in two Center Divisions. Currently, 92% of Facility use is by peer-reviewed funded investigators. Facility use has increased about 10% per year and is projected to increase 5-10% per year during the next Core grant cycle.